This invention relates to new calcium-phosphate-containing mixed ceramics and to surgical cements derived from such ceramics and certain setting components. The cements of this invention have reasonable, and preferably controllable, setting times and are easy to manipulate. By mixing the cementing component and setting component with water, a viscous and cohesive or adhesive paste is formed which becomes hard and sets, preferably in less than about 30 minutes. These cements can be readily used as or in a binder system or as a drug delivery system in granule forms of hard tissue implant materials. The present cements are useful in orthopedic and maxillofacial surgeries and in dental applications.
Bioglass and calcium phosphate ceramics have been confirmed as excellent biocompatible hard tissue implant materials. Among these calcium phosphate ceramics, hydroxyapatite and certain tricalcium phosphate ceramics have been commercialized. Most of these hard tissue implant materials are prepared in either block form or granule form. Similar to ceramic materials in general, such block forms of bioceramic are very brittle and very difficult to shape. On the other hand, the granule form of such materials has mobility problems. In the past many attempts have been made to solve these problems and to expand the medical applications of bioceramic materials by developing binder or cementing materials. Among the materials which have been suggested are collagen, polylactate, Plaster of Paris, polyacrylate, and calcium phosphate grout, paste and cementing materials.
Ideally, the binder or cement system should have the following characteristics: good biocompatibility, be moldable at the surgical site, be easy to manipulate, have a reasonable and controllable setting rate, and be bioresorbable. Most of the binder systems or cementing materials have certain disadvantages. For example, collagen and polylactate can be used as binders in granule forms of hydroxyapatite ceramics or other bioceramics, but such materials can be prepared only as premolded shapes. Plaster of Paris can be moldable at the surgical site, but it is usually resorbed too fast to match the bone growth. Polyacrylate and hydroxyapatite cements are non-resorbable.
The surgeon is most interested in surgical implant cements that can be shaped and hardened in situ. However, such preparations are not yet available. Recently, a number of attempts have been made using calcium phosphate ceramics to prepare grout, paste and cementing materials. Calcium phosphate pastes or grouts which can not harden in situ are useless for hard tissue implant because they disintegrate very quickly, for example, in the presence of water. Several calcium phosphate cements which harden have been proposed. All these cements are prepared by the reaction of single calcium phosphate ceramics with acidic setting reagents. In most cases, these cements are very acidic, which detracts from their biocompatibility. In addition, it is very difficult, if not impossible, to control the setting rate, mechanical strength and bioresorption of these cements.
It would clearly be advantageous to provide new surgical cements.